Numerous applications exist where it is necessary to penetrate a sealed container with one or more electrical leads so as to provide electrical access to and from electrical components enclosed within. One such application for which the present invention has particular but not limited utility is for an electrochemical cell or for an IMD (IMD). Such an IMD may comprise for example, an implantable drug pump, an implantable sensor capsule, a cochlear implant, an implantable pulse generator (IPG) such as those adapted for providing deep brain stimulation, nerve stimulation, electrical pacing therapy and cardiac rhythm management techniques (e.g., for delivering electrical stimulation therapy for various cardiac arrhythmias). All such devices, including discrete electrochemical cells, are intended to be covered under the rubric of IMD. A typical IMD have one or more housing or encasement members for isolating the active contents of an electrochemical cell (e.g., battery or capacitor) which is coupled to the electrical components within and/or coupled to the IMD. The IMD typically has at least two major outer housing members that form a hermetically sealed canister when welded together to provide a hermetic sealed interior space for the components of the IMD.
An electrical lead or terminal pin is electrically connected to the IMD by means of attachment to one or more feed-through assemblies that penetrate the container but maintain the hermetically sealed environment thereof. A typical feed-through assembly consists of an external metal part, or frame or ferrule, into which an insulator solid part typically formed of glass, ceramic, polymer, or glass and ceramic is sealed. Within the insulator, one or more metal leads or terminal pins are hermetically sealed. The hermetic sealing of the feed-through assembly typically is achieved by brazing the components using a brazing metal or alloy. Since the reliability of IMD's, such as IPG's, depends in large part on hermetic sealing of the components of the feed-through assemblies, the integrity of such seals is of paramount importance.
Some of the more popular materials employed to form the terminal pin of the feed-through assembly include tantalum and niobium. Unfortunately, tantalum and niobium are susceptible to oxide growth, which can, depending on its extent, act as an insulator instead of a conductor over the surface of the terminal pin. While it has been proposed to use other materials less susceptible to such oxidation from which to form the terminal pin, such materials pose significant challenges as it is often difficult to braze to such materials and thus difficult to form satisfactory hermetic seals. Often, even when satisfactory brazing to the terminal pins has been achieved, the appearance of the braze has been commercially unacceptable.
Accordingly, it is desirable to provide a feed-through assembly of the type used, for example, in IMDs, which comprises a highly conductive, oxidation-resistant terminal pin. It also is desirable to provide a feed-through assembly that maintains a highly reliable hermetic seal. It is further desirable to provide a feed-through assembly with a commercially acceptable appearance. In addition, it is desirable to provide methods for fabricating the aforesaid feed-through assemblies. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.